1. Field of the Invention
The invention relates to a pressure generating unit, in particular a pressure generating unit that is arranged in the handpiece of a vacuum biopsy apparatus that is embodied as a type of syringe and whereby, by retracting the piston in the evacuated cylinder space when changing over to generating overpressure, the air supply is released by the position of the piston.
2. Description of the Related Art
A vacuum biopsy apparatus may include a pressure generating unit that is connected via a connecting line to a biopsy needle unit that is inserted into the tissue to be examined. The pressure generating unit and the needle unit are arranged parallel in the housing of a handpiece. A vacuum is generated in the needle space for removing the specimen by means of the pressure generating unit.
In order to be able to use the pressure generating unit for generating an overpressure as well, an aeration aperture is provided, and when it is released by the syringe piston, the vacuum that was generated is removed so that the air that has since penetrated can be compressed by means of the syringe piston.
Because not only the specimen is drawn into the specimen removal space by the vacuum, but also tissue fluid is drawn in, when the aeration aperture is briefly released, tissue fluid that has penetrated into the cylinder piston space can flow out into the interior of the handpiece, in particular when the pressure generating unit and/or the handpiece with the needle unit and the pressure generating unit connected thereto is in an unfavorable position. In order to prevent this, it has already been suggested to seal the aeration aperture by means of a sponge that is arranged on the exterior of the piston cylinder. However, this is not sufficient in all cases.